Sensors utilizing individual grains suspended in a matrix similar to a colloidal suspension of very small particles are currently being tested for use as cryogenic detectors of high-frequency electromagnetic radiation (e.g. .gamma.-rays and X-rays) and particles (e.g. electrons, neutrinos and weakly interacting massive particles.) These devices generally are composed of grains of a variety of different shapes and sizes with limited order or control of the shapes, sizes and relative spatial relationships of the grains in the matrix other than generally the maximum size of the grains. The shapes may be irregular, the sizes will vary randomly within a range and their disposition within the matrix will be no more ordered than particles in a colloidal dispersion.
Normally th.e particles or grains in the matrix will not exceed about 100 microns in their largest dimension and will be made from type I superconducting materials.
Such a detector can detect the presence of particles or radiation of sufficient energy, but the sensitivity, efficiency and both the energy and spatial resolution are dependent upon the number of grains, their size and shape, the uniformity of their size and shape and their distribution in space. The accurate preselection of all of these parameters in a detector has not been achieved and probably cannot be achieved using the conventional prior art teachings. A "figure-of-merit" for efficiency is the fractional spread F.sub.s in the individual superheated superconducting-to-normal transition temperatures in a given magnetic field; EQU F.sub.s =(.DELTA.T.sub.c /T.sub.c) (1)
The prior art figure F.sub.s for tin grains, for example F.sub.s =6% approximately for a magnetic field of 0.01 Telsa (T).
Other detectors are described for example in a book titled "Low Temperature Detectors for Neutrinos and Dark Matter" edited by K. Pretzl, N. Schmitz and L. Stodolsky, Springer Verlag 1987.
Another example of a detector using a wire grid detector system is described in U.S. Pat. No. 4,135,091 issued Jan. 16, 1979 to Lanza et al.